ABSTRACT:

The tubular pipes used to carry the oil gas from the deeper reservoirs in the sea bed are subjected to reservoir fluids at high temperatures and pressures. These gases are mainly hydrocarbons, H2S and CO2 and temperatures in the vicinity of 120°C or even higher. In the present work, an attempt has been made to study the behaviour of duplex steel in the simulated atmosphere of oil well by using mixture of 8.00% H2S and 21% CO2 with L.P.G. as carrier gas. The duplex steel coupons did not show any perceptible changes in weight in the simulated gas mixture up to 311 hours at temperature of 1Z00C and also no scale formation was observed. No sulphide was detected by EDAX though the specimen surface got slightly tarnished. The duplex steel coupons subjected to pure HZ 5 at 120°C to Z400C for 8 and Z4 hours showed no appreciable weight change whereas at 500°C and 550°C for the same duration of exposure showed presence of multiple non adherent brittle scales. This indicates aggressive attack of HZS (sulphidation) on duplex steel at high temperature (550°C). An attempt has also been made to standardise the testing procedures of special steels under sour environmental conditions.

INTRODUCTION

Duplex (austenitic/ferrite) stainless steels are a relatively new class of engineering materials used in oilfield applications. They are of much interest because they typically have better "corrosion resistance than 3% Cr and AISI 410 type steels (1). In general, the inorganic materials are more corrosive than organic materials for example corrosion in the petroleum industry is due more to sodium chloride, CO2, H2S than to oil and gasoline. By seeing damage caused by corrosion, it is totally impossible to perform present day operations economically without the use of corrosion resistant material (2).

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